The FIFA World Cup finally kicks off today! Despite my team’s recent Champions League Final defeat to Gareth Bale, this huge global tournament still excites me. The problem for me is that the Venn diagram of ‘my mostly sci-curious friends’ and ‘fellow football fans’ has a pretty tiny intersection, which makes for a long and frustrating month for me. This seems a shame, because there is a huge amount of science in football, one of the biggest industries in the world. Not convinced? Allow me to attempt to convert you to The Beautiful Game through materials science! A lot of money goes into research that funds improvements in every aspect of the game; from engineering better grass to play on, to the material science of football kits. These advances in science have improved the speed and safety of this sport, making it unrecognizable from the game played a few decades ago, when footballers still had other day-jobs.
When approaching any challenge as a material scientist, we assess the activity being undertaken, identify the desired material properties required, and scour a library of known materials for these properties to identify which material, or indeed materials, could potentially be used in this particular application. Then follows experimentation, prototyping and testing, and further iterative improvement of the product before it is launched.
This process has happened with each piece of kit that a footballer wears or uses. Let’s start with a fan favorite – the humble football shirt. So much more than an advertising board and a modesty manager, football shirts have been engineered over the years to ensure that the player maintains optimal playing comfort throughout a match, come rain or shine, so they can perform to the best of their ability. To a large extent, this has been achieved by using man-made polymer materials, often polyesters, whose properties can easily be tailored to requirements.
No one wants to feel weighed down by their attire when they are running around playing football. This is why the materials used in football shirts are very light and very thin. They also need to have a tensile strength high enough to prevent the shirts from ripping too easily in a bad tackle. Despite there being very little material, football shirts are highly engineered. On a rainy day, very little water is absorbed by a polyester shirt (around 0.4% of its weight), owing to the low absorbency of this thin material, unlike a t shirt made of cotton which could soak up a lot of water (around 7% of its weight). When a player gets hot, the shirt can also help keep a player cool and dry. If sweat is formed on the player’s skin under the shirt, the materials that make up the shirt help to physically move this away from the skin. This fabric is known as wicking fabric. Close to the skin, hydrophobic, or water-hating, polymer fibers move the water through or along the fibers and away from the skin by a capillary action, a combination of the physical structure of the polyester fibers and the adhesive and cohesive behavior of water molecules. By having a high density of tiny fibers in contact with the skin, the surface area of this material is vastly increased, allowing it to quickly pull more water away from the skin. The water is moved to and dispersed across the outer surface of the shirt, where it can evaporate off the shirt quickly, once again owing to the larger surface area available for evaporation. This process is further sped up due to the heat of the player’s body.
While some football shirts may have panels of this in specific areas where sweat can be produced, this technology will only work well if these fine fibers are in close contact with the player’s skin. This is why these shirts can be rather form-fitting, as we saw during the last World Cup. This may not however be the only reason that shirts are becoming ever-increasingly ‘bodycon’ in style. Not only can panels of wicking material aid climate control in a player, the right fabric can also physically support the player. Panels of material with specific flexibility, elasticity, or high or low tensile strength can be designed into the shirt to act as support for the player, to help minimize injury, to activate certain muscles via compression, or to avoid the inhibition of movement. The more form-fitting shirts also minimize the opportunity for an opponent to grab a player and bring him crashing down to the ground, speeding up the pace of the game strategically while also allowing players to play at their best.
The materials science doesn’t stop at the shirt. Let’s think about the boots. At a base level, they need to cover the foot to allow a player to run on a pitch and kick a ball. Trainers don’t quite cut it if you want to run fast without slipping on wet grass, and you want to turn quickly without skidding sideways. Studs on the base of football boots can help this. These hard buttons that protrude from the base of the shoe are shaped in such a way that they grip the ground each time a player takes a step, but the player can also move on quickly without having to consciously retract the boot from the ground. The sport is faster than ever before, and players need to run a lot. The boots need to be light so they don’t wear the players out unnecessarily, and of course to allow them to score those famous balletic, airborne goals as demonstrated by Bale in the Champions League Final. They also need to be tough enough to block fast moving balls and kick them hard. Creating materials that are strong, light, and able to protect the foot from strong forces could be a challenge, but by combining a range of materials with different properties, it is possible. Foam insoles to protect the foot from fatigue, strong mesh materials to keep the shoe strong but breathable, areas of reinforcement strategically placed only where needed for ball kicking, and materials that can dissipate the energy of a large force when applied so that the tiny bones in the foot do not shatter (hello, Beckham’s second metatarsal). Each different material here can also be created using polymers, these versatile long-chain molecules that can showcase a range of properties by mixing up the way that they are connected to one another, and therefore the way that they can move and reversibly deform.
Although boots spend most of their time in contact with the ball, let’s not leave the Goalkeepers out here. Even goalie gloves have been engineered to be comfortable to wear and offer a level of protection. They are often made with a layer of material that, unlike a football shirt, can absorb a certain amount of water and hold it within the glove. While this sounds rather squelchy, the water behaves like an insulator, keeping the goalie’s hand’s warm in between handling the ball, ensuring that the muscles in their hands do not get cold. They also need to be flexible. Polymers used in goalkeeper gloves can also be engineered to have a high-friction, rubbery surface, allowing the goalkeeper to better handle a football (is it too soon to presume that Karius was not wearing anything of the sort in the Champions League Final?!), but there is great debate over this, and indeed other sorts of materials science meddling. Would modified kit such as this give players an unfair advantage over other players? It is something that sports governing bodies the world over are having to keep on top of, to ensure that no team is benefiting unfairly from ‘technological doping’, or kit that has been modified in such an advanced way manner that the advantage it could offer the team is deemed excessive.